Field
Aspects of the present disclosure relate generally to the fabrication of memory devices, and more specifically to methods of forming components of magnetoresistive random access memory devices.
Description of the Related Art
Random access memory (RAM) is the most common type of memory found in computing devices. Advances in RAM technology have allowed for an increase in computing power. One advance in RAM technology is the development of magnetoresistive random access memory (MRAM). Unlike other RAM technologies, data in MRAM is not stored as electric charge, but rather by magnetic storage elements, known as MRAM bits. MRAM bits have magnetic tunneling junction (MTJ) structures. MTJ structures are formed from two ferromagnetic layers separated by a thin dielectric layer. The thin dielectric layer is commonly referred to as a tunneling barrier layer. The tunneling barrier layer is designed to be thin enough to allow electrons from one ferromagnetic layer to “tunnel” through the tunneling barrier layer to the other ferromagnetic layer. One of the ferromagnetic layers, referred to as the “pinned” ferromagnetic layer, is set to a specific polarity. The polarity of the other ferromagnetic layer, referred to as the “free” ferromagnetic layer, can be changed by an electrical current. In spin transfer torque (STT) MRAM devices, the orientation of the free ferromagnetic layer can be modified by using a spin-polarized current, which is called writing.
To write a “0,” or a low resistance state, on a bit which was previously a “1,” or a high resistance state, a current is caused to pass from the free layer to the pinned layer. The electrons flowing through the pinned layer attain the majority spin along the pinned layer magnetization and exert a spin torque on the free layer to switch the magnetization direction to align along the pinned layer. To switch to the “1” state, a write current is caused to flow from the pinned layer to the free layer. The electrons flowing from the free layer with majority spin (aligned with pinned layer) pass through the pinned layer, but the electrons with minority spin are reflected back to the free layer. The minority spin electrons then exert spin torque on the moment of the free layer and switch the free layer to align along the minority spin, or anti-parallel, to the pinned layer. A bit state is read by sensing the resistance of the bit and comparing the resistance to a reference resistance, which is usually an average of the high and low resistance values.
MRAM offers the advantages over other types of non-volatile RAM (NVRAM) of being much faster while consuming less power and suffering from less degradation over time. However, current manufacturing yields of MRAM devices are low, while the industry demands that the size of MRAM devices decreases. For example, one obstacle for high manufacturing yields is that some etching processes in the fabrication of MRAM bits corrode the MTJ layers.
Accordingly, what is needed in the art is a new process flow for reliably fabricating MRAM devices.